CD274 and breast cancer: In murine hepatocellular and breast-cancer models, 50 μg ml-1 melatonin lowers tumoural PD-L1 by 40% and expands the CD8+/Treg ratio two-fold, thereby magnifying the tumour-regressing effect of anti-PD-L1 antibodies without amplifying immune-related toxicities (51, 52).